Method of making paper and non-woven fabric from synthetic fibers



, 1.965 R GROSSTEINBECK ETAL 3,200,033

METHOD OF MAKING PAPER AND NON-WOVEN FABRIC FROM SYNTHETIC FIBERS Filed Nov. 1, 1962 FIG-2 FIG! FIG.4

United States Patent 3,290,033 METHOD OF MAKING PAPER AND NON-WOVEN FABRHC FRQM SYNTHETIC FEBERS Rolf Grossteinbcck, Franlrfurt am Main, Walter Schulze, @snahrucir, Winfried Williclrs, Hofheim, Taunus, and Herfried Minder-mania and Gert Tepel, Frankfurt am Mam, Germany, assignors to Battelle-Institut E.V., Frankfurt am Main, Germany Filed Nov. 1, 1962, Ser. No. 234,673 Claims priority, application Germany, Nov. 2, 1961, G 33,481; .lan. 18, 1962, G 34,052; Apr. 27, 1962, G 34,836; July 7, 1962, G 35,413

Claims. (Cl. 162-146) The invention relates to a method for the preparation of paper and non-woven fabric from synthetic fibers and more particularly to a method of bonding the fibers at their crossing points.

Various methods of making such products are known which may be divided into dry processes and wet processes. While the dry processes require special machines, the wet processes may be carried out in conventional papermalting machines.

In the known methods, a binder is generally applied to the fibers or to an already formed sheet or mat, whereby the fibers are bonded at their crossing points. Subsequently, the binder is cured or hardened by a heat treatment of the mat. The thus obtained web has the drawback that each fiber is coated with a thin cured film of the binder and that, therefore, not the original fiber but the binder film largely determines the properties of the Web.

In order to avoid this drawback, a dry process has been developed where a conventional staple fiber is treated with a hydrophobic or water repellant agent and the dry felt of such fibers is sprayed with an aqueous solution or dispersion of a binder. The droplets or globules ofsuch solution or dispersion do not spread on the hydrophobic fiber surface but flow thereon to the crossing points of superposed fibers and remain there suspended. On heating, the water is evaporated and the binder cured.

Such a method cannot be used in the wet process on papermaking machines because an aqueous solution or dispersion of the binder would be flowed away in the wet end of the machine with the Waste water; when applied in the dry end, by spraying, the binder could not penetrate deeply enough into the rather strongly compacted sheet.

It is a principal object of the invention to provide a method which makes it possible to incorporate a binder in paper and non-woven fabrics made on papermaking machinery in such a way that the binder joins the fibers only at their crossing points homogeneously throughout the entire web.

Another object of the invention is to provide a method where the binder is added only in the amount required for bonding the crossing points of the fibers.

A further object of the invention is to provide a method which allows of bonding the fibers at their crossing points in a very simple manner.

T ese and other objects of the invention are accomplished by admixing to the fibers, prior to the formation of a mat or web, a lubricant which is insoluble in water and in the binder, and a binder which at normal temperature, for instance at 20 C., is solid and as little adhesive as possible but is fluid and becomes adhesive at elevated temperature of about 80 to 129 C. In the liquid state, lubricant and binder must be incompatible under the operating conditions, that is they must be insoluble in each other. The fiber mixture is then formed to a sheet which is subjected to a heat treatment in the drying part of the paper machine. Due to the admixture of lubricant and binding agent to the fibers prior to the sheet forma- ICC tion, the additives are distributed very evenly in the sheet as it is being formed.

The term synthetic fiber is employed herein to designate man-made fibers which have a smooth non-fibrillated surface. Also stretched, crimped or hollow fibers may be used. The synthetic fibers include polyarnides such as nylon 66 (hexamethylene diamine-adipic acid condensation product), nylon 6 (polycaprolactam) and other nylon products (nylon 6/ 10; nylon 11); polyesters from dicarboxylic acids, such as terephthalic or isophalic acid and diols or polyols (Dacron, Diolen, Terylene); vinyl polymers and copolymers on Vinyl chloride or vinyl acetate basis (Vinyon); vinylidene chloride polymers and copolymers (Saran); polyacrylics (Dralon; Orlon; Acrylan; Creslan; Acrylast) and copolymers, e.g., of acrylonitrile with styrene; polyolefines such as polyethylene or polypropylene; polytetrafiuoroethylene (Teflon); modified and regenrated cellulose fibers such as viscose, cuproammonium, cellulose acetate; and others.

For lack of a better term, we call lubricants the compounds used to produce the coating film on the fiber which presents the gliding surface on which the molten latent adhesive composition glides along in forms of droplets to collect at the crosing points of the fibers. The lubricant must be insoluble in water and is either liquid at room temperature or must have a melting point below 120 0, preferably not higher than about C. Suitable such lubricants" are rosin and rosin soaps; waxes such as paraffin wax; organic compounds conventionally used as plasticizers such as alkylenglycol esters of alphatic monocarboxylic acids. Also esters of aliphatic and aromatic dicarboxylic acids with monohydric and dihydric alcohols may be used.

The preferred latent adhesive is a polyurethane forming mixture of polyesters and polyisocyanates whose isocyanate groups are blocked by an alcohol or phenol and become reactive only at a temperature of about 100 C. Suitable blocking agents are, for instance, phenol, butanol, aliphatic amines, etc. [see Angewandre Chemie, vol. 59A, pp. 265-266 (1947)].

The polyesters and polyisocyanates useful for the polyurethane formation are well known and described in many publications, for instance, in the book Polyurethanes by Bernard A. Dombrow, publ. by Reinhold Publishing Corp, New York. and in the various publications on Desmodur (:polyisocyanates) and Desmophen (:polyester) by the German Bayer company; see also the article on Desmodur and Desmophen in Rompp, Chemie-Lexikon.

An illustrative list of polyurethane forming polyisocyanates is given in Brit. Patent No. 892,137, pages 11 and 12. Particularly suitable are, for instance, 2,4 tolylene diisocyanate, hexamethylene diisocyanate, triphenylmethane triisocyanate, naphthylen-l,5-diisocyanate, and others.

Suitable polyesters are those of aliphatic'polyols such as ethylene glycols, diethylene glycol, hexamethylene glycol, glycerol, and many others with one or more polycarboxylic acids such as adipic acid, sebacic acid, isosebacic acid, phthalic acids and others.

Another binder which, like the polyurethane forming mixtures, can be spun to filaments is a mixture of epichlo rohydrine resins and oil modified unsaturated polyesters. Examples of such resins and esters are a resin prepared from parts by weight of epichlorolydrine and 5 parts by weight of diphenylpropane, and a polyester of 184 parts by Weight of glycerol and 296 parts by weight of phthalic anhydride, modified with 35 percent of linseed oil. A suitable lubricant for use with this binder is ethyleneglycol stearate.

The lubricant and binder may be added to the fibers tail by the following specific examples.

embodiment of the invention, the fibers are contacted with the liquid or liquefied lubricant so as to receive a thin coating of the lubricant; subsequently, a liquid or liquefied binder is' applied in a similar manner so as to produce a thin binder film on the lubricant coating. In another embodiment of the invention, the lubricant and binder are mixed to a homogeneous mixture which is added in form of a powder or fibers to the slurry of the synthetic fibers. In still another embodiment of the invention, the binder is converted to a filament and coated with the lubricant, whereupon the. coated binder filament is comminuted to staple fiber and added to the aqueous slurry of the fibers forming the mat.

The use of the binder in a filamentary form has the advantage to prevent or reduce the risk that binder is carried awayby the white water during formation of the sheet. Therefore, 'itis not no essary to use an excess of the binder.

If not already added in liquid form, the lubricant is molten in the drying part of the machine and covers the fibers with a thin film. When the temperature is further increased, the binder added in powdery or filamentary form melts also and flows on the coated fiber surfaces to the crossing point of the fibers. The droplets or globules formed at said crossing points are then hardened or cured by further heating and form a kind of knot. The even distribution of the binder in the mat ensures a bonding of the crossing points not only at the surface of the sheet but also in the insidelayers thereof.

The invention will be more readily understood by refer ence to the drawings illustrating on an enlarged scale di-v agrammatically the successive steps of the method of the invention.

In the drawings,

FIG. 1 shows two interc'rossing fibers coated with a lubricant film;

FIG. 2 shows the fibers of FIG. 1 after application of the binder;

FIG. 3 shows the fibers after the binder has contracted at the crossing point and there displaced the lubricant film, and

FIG. 4 shows the fibers as they are in a finished web after removal of the lubricant.

In the drawings, the numeral 1 represents the synthetic fiber, 2 is the lubricant film and 3 the hinder or adhesive. If a batt of fibers, whichhad been pretreatedwith the lubricant and binder, is heated, the binder and lubricant melt on the fiber surface, and the binder film contracts on the lubricant film, which is also fiuid, to drops collecting at the crossing points and displaces there the lubricant. FIG. 2 shows the start, and FIG. 3 the end of this melting period. On cooling the mat, the lubricant solidifies. The lubricant can then be'washed out in a subsequent operation or removed in some other suitable manner. tained end product as shown in FIG. 4, is a web in which the fibers are joined at their crossing points while the remaining portions are free of any coating.

Our novel method can be carried out in conventional paper-making equipment whereby the temperature of the heated rolls in the dryer part of the machine is adjusted to cure the bonding agent.

The invention will be further illustrated in greater de It should be understood, however, that although these examples may describein particular detail some or" the more specific features of the invention, they are given primarily for purposes of illustration and the invention in its broader aspects is not to be construed as limited thereto. For example, the synthetic fibers used in the examples may be substituted up to 50 percent by natural fibers without rep In this example, Dacron fibers were used for the production of a non-woven fabric.

The lubricant was prepared by reacting rosin of a melting point of about 100 C(with ammonia in water. The Dacronfibers were beaten in saidrosin soap solution in essentially parallel arrangement, thencentrifuged and dried, whereby the fibers were coated with a film of the soap and partly joined together.

Subsequently, the fiber lumps were beaten placed in the solution of a latent adhesive, As an adhesive, we used a polyurethane forming mixture of toluylone diisocyanate whose, isocyanate. groups were blocked by butanol and Desmophen 1200, which is a polyester of adipic acid with a mixture of diols and triols, dissolved in acetone and methyl-glycol acetate. After centrifuging and drying, the fibers had then an additional coating of the blocked diisocyanate and polyester. Said coated fibers were slurried in'water and the stock was processed to a sheet on a conventional paper-making machine. When passing the sheet through the dryers,=the lubricant and adhesive mixture melted, the adhesive glided on the lubricant film to the fiber crossing points, and was there activated by evaporation of the blocking agent cured.

, The lubricant was then Washed oil" the fibers. Similar results were obtatined when using as binder the solution of Desmodur AP stable, which is a polyisocyanate with phenol blocked isocyanate groups, which became reactive only at 100 C., in a polyester; As a washing agent, ethylacetate may be used, forexample.

Example 2 In this example, nylon 66 fibers were suspended in dimethylglycolphthalate as lubricant and centrifuged, thereby obtaining fibers coated with about 4 to 6 percent by Weight of lubricant. From these fibers, a stock was prepared containing'about 0.01 to 0.1 percent by weight of solids, and powdered bonding agent was added to the stock in an amount of about 50 percent by weight, calculated on the dry fiber weight.

After the major portion of the water had'been removed in the wet end of the paper machine,-the bonding agent was molten in the heated rolls of the dryer part and glided as droplets to the crossing points of the fibers.- On the further passage of the sheet through the dryer part, said droplets collecting at the crossing pointsvwere activated and cured, producing a firm bond of the fibers at said points. a 1

For the preparation of the bonding agent, a polyurethane forming mixture of blocked toluylene diisocyanate and Desmorphen 210i) (polyester of adipic acid and diols) was'homogenized in a roll mill at elevated temperature without a solvent, cooled to 0 C., and pulverized.

Example 3 As lubricant, we used a paraffin wax having a melting point of 7080 C. The latent binder was the mixture The obof Example 1, which had a melting'point above 1G0" C. Lubricant and binder were homogenized together in a roller mill to a mixture which had not adhesive properties at room temperature. The mixture was pulverized and added to a slurry of Perlon staple fibers in the box. The stock was then processed in the same way as set forth in the preceding examples.

'Thelubricant-binder mixture may also be prepared by spraying the liquefied wax on the powdery binder in a spray-drying procedure. t a i The lubricant-binder mixture may contain about up to 5 percent by Weight of the 1ubricaut,.the balance being binder. About 30 to 50 percent, calculated on dry fiber weight, are added to the fiber slurry.

Example 4' Inthis example, the lubricant-binder mixture was applied in the form of fibers. I

The polyurethane formingjmixture of Example 2 was molten at about C. and extruded through a spinneret to a filament. Prior to winding up, the solidified filament was coated with a film of parafiin wax having a melting point of 75 C. After cooling, the coated filament was wound up; for use, the filament was cut to staple fibers of the desired length.

Said lubricant-binder fiber was added in the box to Diolen polyester staple fibers which had been beaten in a Hollander, and the stock was flowed on the wire of a Fourdrinier. When the sheet passed over the heated rolls of the dry end of the machine, first the lubricant on the binder fiber melted and coated the polyester fibers with a thin film. At increasing temperatures, also the binder fiber melted and separated into droplets which flowed along the lubricant-coated fibers of the sheet to the crossing points of the fibers and hardened there.

Another suitable lubricant-binder fiber is, for instance, a filament of an unsaturated linseed-oil modified polyested coated with ethyleneglycol stearate or other ethyleneglycol ester which in the liquid state is immiscible with the polyester.

Example 5 Viscose rayon staple fibers of a length of 6 mm. were stirred in dimethylglycol phthalate. After about 1 hour, the slurry was centrifuged. The thus obtained fibers retained on their surface about 4 to 6 percent by weight of dimethylglycol phthalate.

Said fibers were beaten in the Hollander with staple fibers of a latent adhesive prepared from a homogeneous mixture of blocked toluylene diisocyanate and unsaturated polyester (Desmophen 950), which had also a length of 6 mm. The ratio of the two types of fibers was 1:1.

The fiber slurry was pumped into the tub and diluted with water to a solids concentration of about 0.1 percent. Said stock was used to prepare on the screen portion of a paper machine a sheet containing the two kinds of fibers in ideal random distribution. After removal of the major portion of the water in the wet end of the machine, the sheet was passed over heated rolls. There, the remaining water was removed, the adhesive fibers melted and the formed droplets of the adhesive flowed along the rayon fibers to their crossing points where they were activated and cured and formed a hard and firm fiber bond.

Example 6 Polyamide staple fibers of commerce (perlon) are dipped at room temperature into a bath of dimethylglycol phthalate. The excess of the dimethylglycol phthalate is centrifuged ofi? so as to leave about 4 to 6 percent on the fibers. The thus coated staple fibers are beaten in the Hollander so long as to be completely individualized. Said stock is passed into the box of a paper machine to gether with the same amount of adhesive fibers cut to staple fiber length of about 6 mm. As adhesive fibers, the same or a similar mixture may be used as described in Example 5. Water is then added in an amount to reduce the solids concentration to about 0.01 percent. The stock is then passed from the box into the wet portion of the paper machine where the sheet is formed and the major part of the water is removed. Thereby, the adhesive fibers are distributed throughout the sheet.

In the adjoining dryer portion, the sheet passes over a large number of heated rolls, the first of which has a surface temperature of about 120 C. The sheet passes through a heating zone of about 150 m. length in a period of about 15 minutes and is then wound up. During the heating step, the adhesive fibers melt and form individual droplets or globules which run on the thin layer of the liquid dimethylglycol phthalate to the crossing points of the crossing points and start there hardening.

Once the cure of the adhesive has started, it continues even at room temperature, but it requires for completion a period of several days. If the sheet rolls are, however, brought in a special heating chamber having a temperature of 150 C., the adhesive is completely cured within about 15 minutes.

Instead of the polyisocyanate-polyester mixtures used as adhesive, other addition polymers or compounds or mixtures capable of condensation or esterification can be used.

We claim:

1. A method of preparing an unwoven web material consisting to at least 50 percent of synthetic fibers, the balance being natural fibers, said method comprising treating the fibers with a water insoluble lubricant material forming in the liquid state a removable film on said fibers, and with a latent adhesive composition comprising essentially a polyurethane forming mixture of a polyester having at least one free hydroxyl group and a polyisocyanate whose isocyanate groups are blocked by a member of the group consisting of alcohols and phenols but are reactive at a temperature of about 0., both said material and adhesive composition having a melting point not higher than C. and said latent adhesive composition having a melting point higher than said lubricant material, being solid at room temperatures and being immiscible With said lubricant material in the liquid state, passing an aqueous slurry of the fibers with said lubricant material and latent adhesive composition through a paper machine to form a sheet, said lubricant material and latent adhesive composition being added in a total amount of 30 to 50 percent by weight, based on the weight of the dry fibers, subjecting the fibers in said machine to a temperature sufiicient to melt and activate said latent adhesive composition, said molten composition collecting as droplets on the film of the lubricant material formed on the fibers at the crossing points of the fibers, and finally curing said composition to a solid binder bonding the fibers at said crossing points.

2. The method as claimed in claim 1 wherein the fibers are first coated with a film of said lubricant material and the latent adhesive composition is added in powdery form to the slurry of said fibers.

3. The method as claimed in claim 1 wherein said lubricant material and said latent adhesive composition are applied in intimate mixture.

4. The method as claimed in claim 1 wherein said lubricant material is an ammoniacal rosin soap.

5. The method as claimed in claim 1 wherein said lubricant is paraffin wax.

6. The method as claimed in claim 1 wherein said lubricant is a dialkylglycol phthalate.

7. The method as claimed in claim 1 wherein said polyurethane forming mixture is applied as a fiber coated with said lubricant material and added to a slurry of the fibers forming the web before said fibers pass into the paper machine.

8. The method as claimed in claim 1 comprising the step of removing the film of the lubricant material after the fibers have been securely bonded by the cured adhesive composition.

9. An unwoven web consisting at least of 50 percent of synthetic fibers, the balance being natural fibers, the fibers being joined at their crossing points only by a cured polyurethane and being otherwise substantially disconnected and free of coating.

10. The method as claimed in claim 1 wherein said intimate mixture of lubricant material and latent adhesive composition is applied in form of fibers.

References Cited by the Examiner UNITED STATES PATENTS 2,680,995 6/54 Forst 162185 2,962,762 12/60 Hartmann 162157 3,049,466 8/62 Erlich 162-157 3,053,609 9/62 Miller 162-157 3,096,231 7/63 Griggs 162-157 FOREIGN PATENTS 572,962 10/ 45 Great Britain.

DONALL H. SYLVESTER, Primary Examiner.

MORRIS O. WOLK, Examiner. 

1. A METHOD OF PREPARING AN UNWOVEN WEB MATERIAL CONSISTING TO AT LEAST 50 PERCENT OF SYNTHETIC FIBERS, THE BALANCE BEING NATURAL FIBERS, SAID METHOD COMPRISING TREATING THE FIBERS WITH A WATER INSOLUBLE LUBRICANT MATERIAL FORMING IN THE LIQUID STATE A REMOVABLE FILM ON SAID FIBERS, AND WITH A LATENT ADHESIVE COMPOSITION COMPRISING ESSENTIALLY A POLYURETHANE FORMING MIXUTRE OF A POLYESTER HAVING AT LEAST ONE FREE HYDROXYL GROUP AND A POLYISOCYANATE WHOSE ISOCYANATE GROUPS ARE BLOCKED BY A MEMBER OF THE GROUP CONSISTING OF ALCOHOLS AND PHENOLS BUT ARE REACTIVE AT A TEMPERATURE OF ABOUT 100*C., BOTH SAID MATERIAL AND ADHESIVE COMPOSITION HAVING A MELTING POINT NOT HIGHER THAN 120*C. AND SAID LATENT ADHESIVE COMPOSITION HAVING A MELTING POINT HIGHER THAN SAID LUBRICANT MATERIAL, BEING SOLID AT ROOM TEMPERATURE AND BEING IMMISCIBLE WITH SAID LUBRICANT MATERIAL IN THE LIQUID STATE, PASSING AN AQUEOUS SLURRY OF THE FIBERS WITH SAID LUBRICANT MATERIAL AND LATENT ADHESIVE COMPOSITION THROUGH A PAPER MACHINE TO FORM A SHEET, SAID LUBRICANT MATERIAL AND LATENT ADESIVE COMPOSITION BEING ADDED IN A TOTAL AMOUNT OF 30 TO 50 PERCENT BY WEIGHT, BASED ON THE WEIGHT OF THE DRY FIBERS, SUBJECTING THE FIBERS IN SAID MACHINE TO A TEMPERATURE SUFFICIENT TO MELT AND ACTIVATE SAID LATENT ADHESIVE COMPOSITION, SAID MOLTEN COMPOSITION-COLLECTING AS DROPLETS ON THE FILM OF THE LUBRICANT MATERIAL FORMED ON THE FIBERS AT THE CROSSING POINTS OF THE FIBERS, AND FINALLY CURING SAID COMPOSITION TO A SOLID BINDER BONDING THE FIBERS AT SAID CROSSING POINTS.
 9. AN UNWOVEN WEB CONSISTING AT LEAST OF 50 PERCENT OF SYNTHETIC FIBERS, THE BALANCE BEING NATURAL FIBERS, THE FIBERS BEING JOINED AT THEIR CROSSING POINTS ONLY BY A CURED POLYURETHANE AND BEING OTHERWISE SUBSTANTIALLY DISCONNECTED AND FREE OF COATING. 